Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.74   10.673%   $215.5246   $215.52   $215.50   $215.50  
  Purchase #2 $208.38   8.337%   $225.7526   $225.75   $225.75   $225.80  
  Purchase #3 $74.27   3.850%   $77.1294   $77.13   $77.15   $77.10  
  Purchase #4 $114.48   5.318%   $120.568   $120.57   $120.55   $120.60  
  Purchase #5 $51.31   6.132%   $54.4563   $54.46   $54.45   $54.50  
  Purchase #6 $119.80   6.548%   $127.6445   $127.64   $127.65   $127.60  
  Purchase #7 $116.46   5.324%   $122.6603   $122.66   $122.65   $122.70  
  7 purchase totals = $879.44       $943.7357   $943.73   $943.70   $943.80